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Micromeasurements on smooth surfaces with a new confocal optical profiler
Abstract
The surface metrology market toady is moving towards non- contact modular computer-controlled system for measuring and analyzing roughness, contour and topography. In this paper we present a new optical instrument based on the concept of confocal microscopy. In this instrument, which is especially suitable for measurements on smooth surfaces, either a pinhole or a structured light pattern in imaged by a very high numerical aperture optical system on the surface of the sample to be measured. The reflected light is observed wit a CCD array and analyzed with different image data processing algorithms. Two different experimental prototypes were developed to allow the measurement not only of surfaces with good accessibility but also of those with intricate geometries, difficult access and small dimensions. Various samples such as high precision optical surfaces, master gratings, and diamond drawing dies were measured. All the results obtained show that the confocal optical profiler is robust enough to provide a surface topography with spatial resolution lower than 1 micrometers and uncertainty about 10 nm. In addition to the replacement of the existing stylus system, there are also important new potential applications for this kind of instrument.
... Confocal profilers have been developed to measure the surface height of surfaces ranging from smooth to very rough [1][2][3][4]. The sample is scanned vertically in steps so that every point on the surface passes through the focus. ...
... The optical setup provides the required matching between pixels of the LCOS and pixels of the CCD array, which in turn behave as confocal apertures [2]. The axial response at each pixel position is calculated from the CCD frames using the appropriate algorithms [3,4]. Because only one or a few points of the surface are illuminated at the same time, in-plane raster scanning is necessary to build the axial response (i.e. the confocal image) at all pixel locations. ...
New material applications and novel manufacturing processes are driving a systematic rise in market demands concerning surface inspection methods and the performance of non-contact profilers. However, analysis of the specifications and application notes of commercial optical profilers shows that no single system is able to offer all the features a general purpose user would like simultaneously. In this paper we introduce a new dual-technology (confocal & interferometer) illumination hardware setup. With this new sensor head it is possible to choose between standard microscope imaging, confocal imaging, confocal profiling, Phase Shift interferometers and white light interferomeiry, by simply placing the right objective on the revolving nosepiece.
... In this paper we present a new optical instrument based on the concept of confocal microscopy 3,4,10 . In this instrument, which has proved to be suitable for measurements on both smooth and rough surfaces, a pattern of slits 5,9 is imaged by a very high numerical aperture optical system on the surface of the sample to be measured. The reflected or diffused signal is observed with a CCD array and analysed with a number of digital image processing algorithms. ...
One of the objectives of surface metrology is to obtain a better and faster assessment of the micro- or nanogeometry of component surfaces. In this way the innovative concept of the profiler is changing towards non-contact modular computer- controlled systems for measuring and analyzing shape and texture of a surface. In this paper we present a new instrument which is based on the concept of confocal microscopy. In this instrument (which may be used for measurements on smooth and rough surfaces) a pattern of slits is imaged by a very high numerical aperture optical system on the surface of the sample to be measured. The reflected or diffused light is observed with a CCD array and analyzed with different digital image processing algorithms. In addition to the replacement of the existing stylus systems there are also important new potential applications for this type of instrument. We present the results obtained in micro- or nanomeasurements of high precision optical surfaces, texture assessment of non-homogeneous liquid depositions and metrology of microstructures such as master gratings and certified calibration standards. The obtained results show that the confocal profiler is robust enough to provide a surface topography with spatial resolution lower than 0.5 micrometer and uncertainty of about 10 nm.
... The surface topography of the discs before and after degradation assays was characterized by the PLm 2300 Optical Imaging Profiler (OIP) from Sensofar, which uses a dual-technology sensor head combining both confocal and interferometry techniques [10,11]. Surface texture was described by average roughness (Ra), rootmean-square roughness (Rq), maximum peak-to-valley roughness height (Rt), and peak count per unit length (Pc), according to ANSI/ASME B46.1-1995 [12]. ...
Enzymatic and microbial degradability of poly(ethylene terephthalate) (PET) and PET copolyesters containing 30mol% of either 5-nitroisophthalic units (PET70NI30) or nitroterephthalic units (PET70NT30) was investigated in laboratory cultures. Two commercial fungal lipases, two bacteria from environmental isolates, and two collection filamentous fungi were tested. The topography of the polymer surface exposed to degradation was characterized by interferometry–confocal microscopy techniques. Biodegradation was estimated by optical and electron microscopy observation, and gel permeation chromatography. Evidence of biodegradation including roughness enhancement, swelling and decrease of the weight-average molecular weight, was only obtained for the case of PET70NT30 cultured with Aspergillus niger. Differences in surface textures were found to be crucial to determine the positive response of this copolyester to biodegradation.
New material applications and novel manufacturing processes are driving a systematic rise in market demands concerning surface inspection methods and the performance of non-contact profilers. However, analysis of the specifications and application notes of commercial optical profilers shows that no single system is able to offer all the features a general purpose user would like simultaneously. Whereas white light interferometers can achieve very fast measurements on the micro and nano-scale without any range limitation, they can not easily deal with steep smooth surfaces or structured samples containing dissimilar materials. PSI techniques allow the user to perform shape and texture measurements even below the 0.1 nm scale, but they have an extremely short measurement range. Imaging confocal profilers overcome most of these difficulties. They provide the best lateral resolution achievable with an optical profiler, but they have a resolution limit, which is dependent on the NA and cannot achieve the 0.1 nm vertical resolution. In this paper we introduce a new dual-technology (confocal & interferometer) illumination hardware setup. With this new sensor head it is possible to choose between standard microscope imaging, confocal imaging, confocal profiling, PSI and white light interferometry, by simply placing the right objective on the revolving nosepiece.
One of the applications, which is considered to be very difficult to carry out with most optical imaging profilers, is the shape and texture measurements of structured surfaces obtained from the superposition of various micro or sub-micrometric layers of dissimilar materials. Typical examples are the architectures of microelectronics samples made up of Si, SiO2, Si3N4, photoresists and metal layers. Because of the very different values of the index of refraction of the involved materials, visible light is reflected in the various interfaces. As a result, some reflected wavefronts are superposed giving rise to interference patterns, which are difficult to understand in terms of surface topography and layer thickness. In this paper we introduce a new method based on non-contact confocal techniques to measure the shape of structured samples. The method is based on the comparison of the axial responses obtained in areas of the surface where there is a layer and in other areas where there is just the substrate. To our knowledge, this approach enables the confocal profilers to measure the thickness of layers on the sub-micrometric scale for the first time.
In this paper we introduce a new optical technique for the measurement of aspheric and free-form optics and moulds. This technique, called confocal tracking, consists on tracking the focus on the sample while it is moved along the horizontal XY axes. Unlike all single-point based techniques, confocal tracking images the surface, which makes it possible to determine the best in focus position within every field of view and to correct the residual tracking errors for each measured point. As a result, confocal tracking provides shape measurements with nm-level accuracy and acquisition speeds of 1 mm/s typically. Depending on sample geometry, high NA objectives can be used, with which it is possible to measure slopes as high as 65°. In addition, because confocal tracking is not a single-point but an imaging technique, it is possible to center the surface to be measured with a very quick procedure that can be automated easily. This step may be particularly relevant for optics with symmetry of revolution. The confocal tracking profiler is a proprietary technology of UPC and Sensofar and can be considered the optical equivalent of a high-accuracy contact profiler.
The first prototype of a technologically improved integrated waveguide absorbance optode (IWAO) was developed and tested with a membrane based on a new H+-selective ketocyanine dye and a cadmium ionophore. It was designed with curved instead of rectilinear planar waveguides. Results demonstrated the suitability of the new IWAOs to be employed as sensing platforms, which confer versatility, robustness, and mass production capabilities besides high sensitivity on conventional bulk optodes, as well as the usefulness of such dyes in developing ion-selective membranes in combination with a selective ionophore. The sensor integration as a detector in a flow injection system (FIA) was proposed to obtain an automated, simple, and sufficiently reproducible (RSD <5%) analytical methodology with a sample throughput of 55 h(-1). Very sensitive optodes were obtained, and detection limits on the order of 20 ppb were achieved. Because of the ionophore employed, the optode system showed excellent selectivity over alkali and alkaline-earth metals with the exception of samples containing lead and cadmium ions, where the membrane responded to both analytes. The proposed procedure combines all the advantages of the FIA systems, the simplicity of optical detection, ion recognition selectivity, and sensitivity of ketocyanine dyes, and the features achieved using the integrated device, which comprise an improved sensitivity and short response times as well as robustness, easy handling, and mass production.
The surface metrology market today is moving towards non-contact modular computer-controlled systems for measuring and analysing contour and topography. In this paper a new optical profiler based on the concept of confocal microscopy is demonstrated. A visible laser beam is focused with a high numerical aperture optical system onto the smooth surface of the component that has to be measured. The reflected light signal is observed with a CCD array and analysed with an image data processing algorithm. Different reference surfaces with flat and round geometries have been measured. All the results obtained show that the confocal optical profiler is robust enough to provide surface topographies with spatial resolution and 10 nm repeatability. These figures have been proved over very high measuring ranges even when the local surface slopes reach values close to . Despite the problem caused by the lack of standardization concerning the non-contact profilers, there are still a lot of new important applications that could be developed for this kind of instrument.
Le marché de la métrologie des surfaces s'intéresse actuellement aux systèmes modulaires sans contact, contrôlés par ordinateur, pour la mesure et l'analyse de la rugosité, des contours et de la topographie. Cet article porte sur la démonstration d'un nouveau profilomètre optique basé sur le concept de la microscopie confocale. Un faisceau laser visible est mis au point focal avec un système optique à grande ouverture numérique sur la surface non rugueuse à mesurer. Le signal lumineux réfléchi est observé avec une caméra CCD et analysé avec un algorithme de traitement d'images. Plusieurs surfaces planes à géométries douces ont été mesurées. Toutes les mesures relevées démontrent que le profilomètre optique confocal est suffisamment robuste pour obtenir des topographies avec une résolution spatiale de et une répétitivité de 10 nm. Ces figures ont été vérifiées pour des grandeurs importantes, y compris avec des déclivités locales proches de . Malgré le problème lié à l'absence de standardisation des profilomètres sans contact, il y a encore une grande quantité de nouvelles applications à développer à partir de ce nouvel instrument.
Virtually everyone has used an optical microscope, if only to dissect a frog in school or to observe the life forms in a drop of pond water. The optical microscope is a powerful research tool in many areas of science, such as biology, geology, medicine and, more recently, semiconductormetrology. As the need to visualize submicron structures has become more pressing, several new types of microscopes have been developed—for example, the confocal scanning optical microscope, the scanning acoustic, the scanning electron and the scanning tunneling microscopes. In microscopes based on this principle a defocused image disappears instead of blurring, allowing the user to independently image different layers of transparent materials.
This review paper is concerned with the imaging properties and major uses of scanning optical microscopes. It is shown that
the confocal scanning microscope exhibits a form of super-resolution and that the instrument in general has great application
in nonlinear microscopy and the inspection of electronic devices.
A real‐time confocal scanning optical microscope is described. It is capable of generating 640 frames per second with 7000 lines per frame. It achieves this speed by simultaneously illuminating several thousand pinholes arranged in a spiral pattern on a rotating disk. An optical isolator is used to eliminate reflections from the surface of the disk. This type of microscope should have the same range and transverse definitions as a standard, single pinhole, confocal microscope.
A CCD-based confocal microscope system that is used to measure accurate three-dimensional surface profiles is reported. For a field of view of 500 µm, surface samples spaced at 12 µm on smooth specular test objects are simultaneously resolved in depth to ~ 1 µm (depending on the surface being observed). A precision of 0.1 µm is obtained for a mirrored surface for a field of view 400 µm wide. Simple scaling and sampling results permit these results to be extended to other apparatus dimensions and range sampling intervals.
The on-axis intensity response of a confocal scanning optical microscope was measured for an objective of numerical aperture 0.9. The data compare favorably with theoretical calculations obtained by numerical integration of the standard theory, provided that lens aberrations are taken into account. The invariance of the shape of the central lobe to surface roughness and tilt is also demonstrated.
Microscope using tandem scanning of reflected light for image contrast and sharpness for semitransparent materials